I take it you are not much of a science-fiction reader.
I was as a child and teen, even through much of my twenties.
I don’t have much time to read now, and what I do tends toward non-fiction.
I also read a fair amount of sci-fi, syfy, and fantasy. Aliens that can intuitively use FTL is firmly in the latter category, well behind Star Trek.
There is nothing wrong with fantasy, I just don’t use it when I am evaluating ideas that are based in the real world. Not that you can’t learn from fantasy. The Dresden Files had a significant impact on my life and world outlook, but it’s not because I learned to do magic from them.
When discussing the real world, I tend to want to stick to either non-fiction or extremely hard science fiction. I’m happy to entertain ideas of FTL or infinite vacuum energy sources and the like as hypotheticals, but don’t depend on them to evaluate actual likelihoods.
Always been a big fan of Sagan and agree that he was massively influential. Sagan was a scientist with the heart of a poet. If he got a few minor points wrong against the tidal wave of things he got right, I forgive him—he was human, not a late-model chatbox.
An extraterrestrial specie’s biology and genetic makeup is likely to be more dissimilar to humans than humans are to trees. ETs may have developed intelligence through convergent evolution, but how they think would be completely alien to us.
But still, no matter how smart ETs are, they have to abide by the same physical laws of the Universe that we do. There are some things that may be impossible to overcome (probably FTL travel for example), and there may be some things that are just too costly or dangerous for any civilization to pursue (like extra-stellar expansion).
The argument that “it only takes one” is meaningful if we are talking about very large numbers. But, we’re not. We’re not talking about infinities in time or space, we’re talking only about advanced intelligence that may have developed within the Milky Way galaxy (if we agree intergalactic travel is fantasy) and within some fraction of ~14 billion years. Sure, that’s a large number of star systems ( [Sagan] billions and billions [/Sagan] ), and a large chunk of time for life to emerge. But, if you agree that the emergence of advanced intelligence is most likely very rare (even if simple life is not so rare), then we’re likely to have some, but not a lot of advanced civilizations in our galaxy, in our time frame.
I believe there are advanced civilizations in the MW, but I’m not surprised we haven’t heard from them yet.
Would a visit from an extraterrestrial necessarily spell doom for humans? Not if they just pulled over onto Earth to ask for directions. Otherwise, we’re toast.
But, if we could choose one ambassador to greet the aliens, I wish it was Carl Sagan. Unfortunately, he died. So, my next choice is Carrot Top the comedian. Maybe his silly prop humor would make them hightail it away and never look back.
I’m always skeptical of the fine tuning that is required for this. That there are some civs out there, but not enough to be dealing with very large numbers of them.
There are a lot of potential places for life to arise and develop into a spacefaring civilization in this galaxy, billions of them. For the odds of intelligent life arising to be exactly enough that there are dozens or hundreds, but not millions or tens of millions, is, IMHO, very unlikely.
And if we are talking about millions, then we are talking about numbers high enough to wonder why we are unique, why we are the only species with the capability and drive to expand into space.
If you think the great filter is in front of us, that while we are able to see a realistic future with us out into the galaxy, it is not to be for some reason, then once again, we are dealing with very large numbers, so whatever is going to wipe us out needs to be something that no species is able to avoid, as it only takes one.
The only way that an extraterrestrial visit doesn’t destroy us is some version of the Zoo hypothesis, where our world is being carefully isolated and will not join the galactic civilization until we are ready, though I find this hypothesis highly unlikely.
Any other encounter leaves us destroyed by either intent or neglect.
I’d nominate (Lord) Chuck Nice, Neil Degrasse Tyson’s usual co-host for Star Talk Radio.
This sequence from Cosmos still gives me chills, almost a religious experience, I have never forgotten it.
He was right about that happening, but off by about 20 years as to when we would start seeing real world effects.
It’s because we see no signs of advanced extraterrestrial life that causes me to believe there are not millions of them in existence in the MW. If there were, surely we would have seen some evidence by now. Unless you believe the millions are purposely avoiding us, which I find unlikely. Maybe some would hide, but not all.
We do have evidence of one [almost] interstellar species (us), so we know advanced civs are possible.
Therefore, I don’t believe there are millions since we see no evidence of any of them, which I would expect. I also find it unlikely that advanced intelligence occurred just once, given the billions of opportunities to do so. So, by default, that leaves a few in existence, by my way of thinking.
A few could be dozens, hundreds, or thousands.
IMHO the big bottleneck is with the presumed ease of interstellar travel. People debate the Fermi paradox as if that last part were something trivial, citing the fact that a few million years is the blink of an eye when one has billions of years to work with. I get the time scale differences, but I still don’t get how we can wave away the difficulty by increasing the time scale. So yes, there’s probably other intelligent life out there. And other than a few things like their version of Voyager, they’re almost certainly stuck in their solar system.
We are pretty remote. There may elsewhere be two civilizations close enough together to have made contact.
Actually my position is that there are not millions, exactly as you say, we would have noticed them by now.
And that’s what requires the fine tuning. Just enough that there are “a few” but not enough that we notice them. With 100 billion stars in the galaxy, that means that the chances of intelligent life arising is somewhere between 1 in 5 billion to 1 in 20 billion. That’s a pretty narrow range, one that has no justification to be that precise.
That has a less fine tuned range. Anything from 1 in 100 billion to 1 in tree(3) would give us a galaxy that looks exactly as it does to us. If the odds against intelligence occuring are extremely high, then it will still happen somewhere in the universe, and wherever it happens that intelligent life will find itself in an otherwise uninhabited observable universe.
So, we don’t know the odds of intelligent life arising, we can only put a cap on it at 1 in a few hundred million or so, otherwise we’d see them. However the space of odds that mean that there are a few is infinitely smaller than the odds that mean that there is only one. What I find extremely unlikely is that the odds fall into that infinitesimal range, rather than the infinitely larger range.
Start getting into thousands and we start getting into, “It only takes one” territory. But even the range of dozens to thousands still only widens the odds by a little bit, an infinitesimal bit compared to the odds that give us exactly one.
If we are talking about the infinite universe, then I think that there are an infinite number of intelligent species out there, in all stages of development, from stone age to K4. However, once again, the odds of them being within a hundred billion light years, within the cosmological horizon, is infinitely small compared to the odds of the closest being quintillions of light years away. The further away, the higher the odds that something is out there.
That’s where I’m coming from. The odds that we are alone are infinitely larger than the odds that there are a “few”. Without some evidence that constrains those odds, I tend to lean towards the infinitely more likely than the infinitesimally likely.
Okay, so you and I and a small group go to an asteroid out past Neptune. It’s a dozen miles across or so. Over a few centuries, we develop into a nation of tens of millions. We decide we want some space, so we head out a bit further, then a bit further, all the while having small groups leave our asteroid for others passing nearby. One day, we realize that we are closer to the neighboring star than we are to Sol. Over the next few centuries to thousand years, we will fill up that solar system, and then find ourselves entering the influence of the next one over.
Then one day, a few million years down the line, you find that you’ve made it to the edge of the galaxy and the whole thing is full.
The idea of people hopping into a spaceship and traveling to the habitable planet the next star over is pure science fiction, but for some reason, it is what people always seem to fall back to when they try to argue against expansion. Of course that’s not realistic, it’s science fiction. But it’s also not the scenario that is presented, so the objections to it are irrelevant.
If we ever settle an asteroid, our future of filling the entire galaxy is all but ensured. So the only argument that is relevant is one that shows that no one can ever settle asteroids, human or alien. I’ve yet to see a compelling one.
I agree many folks hand-wave away the presumed ease of interstellar travel, and I would expand on that. It may be technically easy for an advanced civilization to travel interstellar, but would they want to, to any great extent? Some points to consider:
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What’s to be gained from traveling further than a few local stars away? I can see why an advanced civilization (AC) would want to expand into an area that included a few local star systems, and perhaps beyond the dangerous reach of their home star going nova in the future. And maybe they’d want to harness the energy of a couple local stars (K2 civs). But, what’s to be gained by traveling much further than that? Conquest of the galaxy? I don’t buy it. Central control would be impossible, and rogue speciation could come back to bite them.
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Exploration? If an AC is millions/billions of years more advanced than us, not only would they have interstellar ships and possibly self-replicating drones, they would also have telescopes millions/billions of years more advanced than us, too. Why go to the expense (and long time travel and return) of sending ships and drones to explore when you can learn everything you want to learn simply by using your super-duper telescopes?
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Acquisition of resources? Would an AC need, or want resources from many light years away, that are costly to get and time consuming to retrieve? They’ve probably perfected advanced Martian alchemy and can synthesize any elements they need from basic particles close to home.
I believe the Great Filter is either the emergence of life, or the emergence of advanced intelligence from simple life. I’m betting on the latter, and hope that I’m right because I want to see some alien slime mold in my lifetime.
And, I hope the Great Filter is porous because I want to see some Klingons in my lifetime, too.
Getting to an asteroid would only take about 1 year. Maybe about 10 years to get to Pluto. If we needed to we could make stops along the way on the moons of Jupiter, Saturn, Uranus. and Neptune. But after that we’re taking a whole different level of tech. Just to get to the Alpha Centauri system would likely be thousands of years. We obviously don’t have the tech to maintain a generation or cryostasis ship that will survive for multiple millennia in deep space, and still have the energy to stop once it reaches Alpha Centauri. I can’t even imagine what sort of tech we could develop that would enable it short of the stuff of science fiction. Getting to Mars, the asteroids, the moons of the gas giants, or Pluto, however is possible. We just don’t have the political will to do so. I don’t think even all of mankind working together, however, is enough to bridge the gap to make it to the next solar system. At least not with our current tech or near future tech.
ETA. It’s that last step when the journey goes from lasting a few years to lasting several millennia which seems impossible, no matter how advanced our tech gets.
From what I understand the denominator is also a lot smaller than the several billion stars in the Milky Way. The inner galaxy is probably uninhabitable thanks to the gravitational forces from Sagittarius A*, and that’s where most of the stars happen to be. I think we can also safely ignore other galaxies as well.
Here’s one cite about star density in our galaxy. The galactic core is around 10 million stars per cubic parsec. In our area of space it’s 0.2 stars per cubic parsec.
https://www.astronomy.ohio-state.edu/ryden.1/ast162_7/notes31.html
If we rule out all those stars in the center as unable to develop life due to being too close to a super massive black hole and too close to each other, the denominator gets a lot smaller.
It’s not the gravity per se that is dangerous in this volume, it is the risk of colliding stars and other material orbiting the SMBH. Our galactic core is fairly quiet now, but probably in the past there has been a lot more activity in this region due to collisions and debris. If (as seems likely) our galaxy has ever been an active galaxy, with fast-rotating clouds of matter orbiting the central hole, emitting dangerous radiation, then the central core would have been a very challenging location for our kind of life.
On the other hand, maybe some kind of resilient lifeforms may thrive in such an environment. If so they would have little in common with Earth life.
Once again, you are talking about a civilization, not individuals or small groups. People settle in one area, and as that area builds up, people settle a little further out, and then a little further. Rinse repeat.
What is your reason that people will one day just decide that there are enough people, and so they will no longer have children themselves? That the civilization is big enough, so they will stop building anything?
No, no one has said anything about that. That’s pure sci-fi trope.
Well, the resources that are there, of course. We will always want more. What point are you saying that people will say, “Oh, we’ve got enough, no need to continue to expand.”?
And once again, it’s not a matter of retrieving them. They would be used in more or less the location that they are found.
I’m not sure what you mean by that, but probably not. It will always be harder to synthesize elements than to collect them, and you’d need something to synthesize them out of, as well as the power needed to do so.
Once again, as I have said, it wouldn’t be “we” traveling from one asteroid to another. It would be a group that has settled on an asteroid. As they fill it up, or just want to, some of them travel to other nearby asteroids and settle them. They get further and further out, and eventually, they are within a different star’s sphere of influence.
Like I just said in the post you replied to:
Once again, that’s the whole point. It wouldn’t be all of mankind working together, it would be the effort of small groups.
Getting into space in the first place is a massive undertaking that requires a significant amount of the resources of the planet. Once you are up there and have in situ resource utilization, individuals and small groups can expand with very little if any assistance from the rest of mankind.
And it’s exactly that last step that you have brought up that I have repeatedly said isn’t what is actually relevant. There will be no one embarking on several millennia long space voyages.
Now, OTOH, if an asteroid settlement decides to get a jump on things, they could do so. They can intentionally head out towards another star, rather than just expanding into their local environment. A fun way would be to adjust their orbit around the Sun in order to go on an extremely elliptical orbit as close to the sun as it can stand, and while it is close fire off a shit ton of nukes as an Orion drive to take advantage of the Oberth effect. It’ll still take centuries if not millennia to get to the next star, but they aren’t in a little spaceship, they have an entire world, with area equivalent to continents and resources equivalent to several times that on Earth to make the trip.
I don’t know how often that would happen, and how much growth would be simple incremental expansion, but over time, both will eventually fill up the galaxy. Sure, it may take a few tens of millions of years, maybe even a hundred million, but it’ll get the job done.
It’s really more that there are so many stars, and they tend to be big and short lived, that you’d have novas going off uncomfortably close fairly often.
Stars almost never collide. The only time you ever really see it is in binary systems that have spiralled down. One star just coming along and smacking into another star is basically unheard of. OTOH, stars can pass close enough to mess with the orbits of a stellar system. Even if it doesn’t pass close enough to make any inhabited planet fall out of the goldilocks’ zone, it may still disturb enough Oort cloud material to post a significant danger.
So, yes, a fair amount of speculation puts a habitable zone around the Milky way that is where we are. Go towards the core, and things get more dangerous, go away from the core, and heavier materials start to become sparse.
That kind of incrementalism just isn’t realistic. It is difficult for people who have grown up on a diet of space opera to really grasp, but the scale of interstellar space is enormous (literally astronomical), and the resources and energy required to transit these scales using the momentum transfer mechanics that are offered by our current understanding of physics is just prohibitive even before you get into the details of how to make an automated probe reliable enough to function after many thousands of years of exposure or the thermodynamics of rejecting all of the waste heat developed from a high performance propulsion system. Even if we had an endless amount of resources ability to achieve any speed necessary to transit to even stars in our local neighborhood is daunting. Quoting myself from a prior thread on this topic:
Let’s look at the mass ratios involved, just using specific impulse numbers. At Isp = 5000 s, getting to 0.01c* would require around 3x1026 kg of propellant for every kg of payload. Decelerating back down (presuming the destination system is relatively stationary compared to Sol) would require about 9x1052 kg of propellant for every kg of payload. If we improve the performance to 20,000 s (a realistic limit for a spacecraft we could actually construct) the ratios are only 4.2x106:1 and 1.7x106:1, respectively. Only at around 80,000 s do the numbers start to get remotely reasonable (45:1 and around 2000:1). Even at 100,000 seconds, you are looking at 21:1 and 440:1.*
Without some fundamental advances in basic physics of propulsion or some other method of going around spacetime instead of through it, sending even hypothetical automated, self-replicating probes would not just take a few million years but tens or hundreds of millions. And that assumes that some alien civilization would be motivated to do so for…reasons? It can’t be commerce, and not conquest in any conventional sense. Exploration? By the time such probes would reach systems that are beyond the range of advanced telescopes and other passive methods of observation, such a civilization would likely advanced to a new phase or collapsed completely. To say “Hi” to cosmic neighbors and exchange ideas? Even a civilization that wasn’t wary of the potential hazards of contact couldn’t have the expectation of having anything like a conversation, and the issues of even communicating over distances of more than a few tens of lightyears with electromagnetic waves are daunting and expensive in terms of the absolute energy requirements. Certainly sending bags of organic chemicals and water is manifestly unrealistic, and even some mechanized or more robust basis for alien life would have to cope with millennia of exposure to highly ionizing galactic radiation. This isn’t to say that there isn’t some loophole that provides some non-momentum exchange propulsion or ‘wormholes’ around the plenum of normal spacetime, but even if such possibilities theoretically exist they make require more energy than is practicable.
It isn’t that we have to be remote. The Milky Way galaxy has enormous volume (if we ignore the central bulge and use an average disc thickness of ~1,000 lyr, it is on the order of 5x12 cubic lyr), and if it were solidly packed with civilizations in non-overlapping spheres each 1,000 lyr in diameter, you could fit well over five million civilizations which are far enough away from each other that any possibility of communication or incidental detection is extremely unlikely, notwithstanding that the majority of star systems in the galaxy almost certainly could not support the development of life as we might recognize it. And while it’s certainly possible that an industrial civilization could last more than 1,000 years, to have two that have arisen in the same time period is enormously unlikely even if we make the assumption that industrial civilizations routinely develop within any 10 million year timeframe; with that assumption and a 1,000 year lifespan for an industrial civilization before it (collapses or advances to something unrecognizable) gives an estimate of ~500 active civilizations would give an average distance of around 5,000 lyr, meaning they would never communicate with one another by any means of conventional physics. Extrapolating, even if we assume that industrial civilizations are common and last for many thousands of years, it is still statistically unlikely that we would be close enough to one to observe incidental signals or be able to communicate in the timescale of a human lifetime.
And I know someone is going to put forth the argument that an industrial civilization would advance up the “Kardashev scale” and at least leave residual megastructures that would be observable from their interference with normal spectral emissions of a star, but that is purely an assumption that is not only unvalidated but unlikely once you delve into the details of what it would take to build a megastructure, and what motivation a civilization would have if they had the resources to do so. The notion of building such a structure for agriculture, or to collect the energy from their star, or living space is inconsonant with what a really advanced civilization would likely do because if they had the capacity to engineer those structures they’d likely just put it into advancing themselves to require less resources or space. The Kardashev scale is kind of like late 19th century Victorians imaging 21st century travel and spaceflight as being bigger zeppelins and cannons firing steel casings with ‘expendable’ operators into orbit. However an advanced civilization will develop is likely as unimaginable to us today as our current technology would be to a Saxon or Viking, and assuming that technology must develop as a linear extension of current methods is essentially the only prediction that we can say is certain to be wrong, as is any narrow restriction on how alien civilizations or technology must develop, or how they might think and communicate.
Stranger
Yeah, that’s true. I really meant that stars would collide with the gas and debris in the accretion disc around an active nucleus, and spiral inwards to become disrupted themselves. About 10% of galaxies have an active nucleus; does that mean our own galaxy has been active for 10% of the time? Probably not, but it might work as a rough guess.
Maybe my picture if interstellar space is completely incorrect. From what I understand, however, once we get past Pluto there’s a few smaller things out there in the Oort Cloud, and some hypothetical Planet X around the size of Uranus and Neptune. Even that will taper out well before getting halfway to Alpha Centauri, where we could maybe start using the Alpha Centauri Oort Cloud. Overall it just seems like there isn’t anywhere close to enough stuff in usable form to be able to survive, let alone thrive long enough to build a new civilization.
The first question is where will these settlers / explorers / voyagers, whatever you want to call them get their resources from? That far out they can’t rely on energy from the sun, and by the time they get close enough to Alpha Centauri to use solar energy again they would have already completed the hard part of the journey. Chemical energy is going to be difficult. There’s plenty of stuff like methane out there but no molecular oxygen (or fluorine or chlorine even if we develop the tech to stabilize the stuff and use it for oxidative purposes) to use for burning that fuel. Nuclear is probably going to be equally difficult, because even if they can find some uranium or thorium out there (and that far out I’m betting that stuff is a lot more rare and difficult to get at than it is here on Earth), how are they going to get the energy to concentrate it into a usable form? And that’s not even taking into account or nutritional needs. Photosynthesis is probably viable on Mars, but past that it’is out of the question. We can’t rely on stored up energy carried with the initial crew that left Earth. Maybe with enough advancements and genetic engineering of plants we might be able to get as far as terraforming small areas of Mars, but past that we’re going to need something we aren’t even close to developing. Then there’s all the other stuff we would have to find and process to make the spaceships. Is there aluminum, silicon, titanium, iron, nickel, copper, etc. out there in the Oort clouds? Sure. But how are we going to build factories to process all that stuff into the spaceship parts that are needed for the next leg of the journey? How will we know that the next stop along the way will have everything we need to continue the journey? It all seems way to difficult to make the journey by using such a stepping stone approach.